1. Field of the Invention
The present invention relates to a control for disabling and restoring the operation of a voltage detection circuit.
2. Description of the Related Art
In these years, SD (Secure Disk) cards have widely been used more and more as external storage devices that are small in size and excellent in portability and information security. According to physical specifications of the SD card, the operational power supply is defined in two stages. For the purpose of operational compensation, two kinds of power supply voltage detection circuits need to be provided. Normally, since two voltage detection circuits are always activated, operation power is always consumed by the two circuits.
In the conventional memory card such as the SD card, there is no control circuit for disabling either or both of the two voltage detection circuits. Consequently, power is consumed by these circuits even in the standby state in which the memory card is not activated, and the operational efficiency is low.
Jpn. Pat. Appln. KOKAI Publication No. 5-74136 discloses a technique for increasing the life of a cell for a memory card, in order to reduce power consumption of the memory card.
According to the technique of KOKAI 5-74136, cell voltage detection in the memory card is performed only in a short time period in which external power is supplied to the memory card. Specifically, to achieve this, a cell is connected to a switch-operable element, and an output of this element is delivered to a cell voltage detection element. An output of the cell voltage detection element is supplied to a latch circuit, and an output of the latch circuit is delivered to a connector of the memory card.
In this prior art, however, a detected value is held by the latch, and flexible power supply control management of, for example, disabling one of the voltage detection circuits cannot be performed. It is still difficult to enhance the power consumption efficiency.
As has been described above, in the prior art, there is no control circuit for disabling the voltage detection circuit of the memory card. Thus, there is a problem that power is always consumed even in the standby state in which the memory card.